1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, printer, facsimile machine, or multifunction device (MFD) combining several of these capabilities, and more particularly, to a fixing device employed in such an image forming apparatus.
2. Discussion of the Background Art
A fixing device installed in an image forming apparatus such as a copier, a printer, etc., is known that employs a pipe-shaped heating member made of heat conductive metal disposed opposite an inner circumferential surface of an endless fixing belt (i.e., a fixing member) and around which the fixing belt slides as it is rotated, as described, for example, in Japanese Patent Application Publication No. 2010-96782 (JP-2010-96782-A). Specifically, the pipe-shaped heater itself is heated by a heat source to heat the entire endless fixing belt to reduce defective fixing, even in a configuration in which a warm-up time and a first printing time are minimized to speed up operation of the image forming apparatus.
The fixing device of JP-2010-96782-A is composed of the endless belt, a fixed member fixedly disposed on an inner circumferential surface side of the endless fixing belt while pressing against a rotating member via the endless fixing belt and forming a nip thereon, and the pipe-shaped heating member fixedly disposed on the inner circumferential surface side of the endless fixing belt having an opening (i.e., a concave portion) opposed to the rotating member (i.e., via the nip). Also included in the fixing device of JP-2010-96782-A is a heater located inside the pipe-shaped heater and a reinforcing member to reinforce the fixed member. Hence, when a toner image borne on a recording medium is transported to the nip, it is fixed thereon under heat and pressure at the nip.
JP-2010-96782-A further discloses a technology of using a pair of stay bolts as a holder to hold and maintain a shape of the pipe-shaped heater near the opening to prevent the opening from expanding near the nip due to the spring-back tendency of the metal from which the heating member is formed.
However, although occurrence of the problem caused by deformation of the pipe-shaped heating member can be successfully prevented by use of such a holder, the number of component parts increases, thereby complicating assembly and somewhat limiting the range of design choices.